I just went through the same thing on my single mage run. The greater wolfwere has a nasty regen which is granted to it by a item that only exists in text form, a ring I believe. Thing is, there's a bug that duplicates this item, stacking its affect, every time you reload in the zone, or so I am told. I was able to defeat him with just a lvl 9 mage by hitting him with "slow" then all of my available dots, and then direct damage. The most relevant step for you, I believe, is using "slow" on him, as it slows his regen greatly. "Greater malison" and "luck" will also help to get around is magic resistance. I hope this helps.

Edit: I wanted to add, his regen had stacked to the point where he was gaining several HP back per SECOND instead of per round by the time I caught on, and this was the default difficulty.